Answer for this queation

The RPM meter, or Tachometer, on your dashboard is used to show the driver how many revolutions per minute your engine is rotating at. This is to show the driver when he is reaching the mechanical limits, redline, of the engine.

If a driver in a manual transmission car does not shift before hitting the Redline of the engine they could damage their engine. That’s why nowadays automatic transmissions typically protect the car by shifting before the redline automatically. Also in modern computer controlled cars there is a fuel cutoff at Redline where the computer will stop feeding fuel to the engine before it would be damaged so the driver cannot accidentally exceed the redline.